In the cramped, oak-panelled confines of courtroom 13, a gripped public gallery listened last week to an existential tale of celebrity grief. Giving evidence at the High Court in her case against the Mirror, Naomi Campbell - supermodel, novelist, restaurateur, pop singer and bottled scent - was twice moved to remind the court that she was also a 'human being'.

There were a number of reasons she may have felt it necessary to confirm her species. She might, for example, have wanted to draw a clear distinction between herself and her fans, one of whom she was seen on film in court describing as 'an ugly bitch with the head of an alien'.

More generally, she could have been making the point that while celebrities such as herself appear to inhabit another planet, they nevertheless originate from this one. But perhaps her main intention was to emphasise that, despite the capricious attitude she famously displays to many of her fellow humans (to say nothing of endangered furry animals), she is still entitled to protection under the Human Rights Act (HRA).

Two other all-too-human celebrities also came under the legal spotlight last week. Jamie Theakston, the BBC presenter, was the subject of a landmark ruling involving the rights of prostitutes to name their clients. And lawyers for an unnamed footballer appeared before the court of appeal to defend the injunction he gained last year, preventing two women from publishing their 'kiss and tell' stories.

These cases form part of a series of recent high-profile attempts to establish a new right of privacy for celebrities under the terms of the HRA, which came into force in October 2000. Last year the court of appeal found that Catherine Zeta Jones and Michael Douglas had a 'powerfully arguable case' for invasion of privacy, after Hello magazine published unauthorised photographs of the couple's wedding. Subsequently celebrities such as Anna Ford, Sara Cox and Amanda Holden have sought protection from the press under the HRA.

Campbell is suing the Mirror for breach of confidence and unlawful invasion of privacy, following the newspaper's exposure of the model in February last year as a member of Narcotics Anonymous. Thus her appearance in court marked a head-spinning collision of contemporary obsessions: models, celebrity, the media, drugs, therapy and the culture of confession.

Yet at the centre of Campbell's claims and the Mirror's counter-claims, shrouded by arcane points of legal debate, lies a simple question: should the propagation of a celebrity's fame disallow his or her right to privacy?

For Piers Morgan, the editor of the Mirror, the answer is equally straightforward. 'Celebrities who regularly invade their own privacy like Naomi Campbell,' he told the court, 'abrogate their rights to privacy.'

Morgan was an impressive witness - eloquent, impassioned and witty - but he is also a man with a track record of dubious editorial decisions, including running photos of Countess Spencer in a psychiatric hospital, and buying shares trumpeted by his own newspaper in the City Slickers' scandal.

As such, he is no more an exemplar of journalistic responsibility than Campbell is a paragon of celebrity diffidence. An unkind observer might almost characterise the two main witnesses in this court case as an unprincipled answer to a question of principle.

But so what? It's their beliefs, rather than their credibility, that are really the issue. For both represent extreme opposing positions on the role of celebrities in public life.

Morgan has recently become the country's most vocal critic of celebrity culture, even as he continues to promote it. A former showbiz correspondent with the Sun , he appears increasingly unwilling or unable to disguise his contempt for the machinations of fame.

In the wake of 11 September, the Mirror began a campaign of revealing the controlling demands celebrities make on the media. Although in court, when Morgan spoke of Campbell 'forcing' newspapers to run her photograph, it turned out that her devious manipulation of the media amounted to nothing more sinister than holding a press conference.

The point is that newspapers such as the Mirror do not feel free to cover celebrities such as Campbell, and celebrities such as Campbell feel unable to escape the forensic attention of newspapers like the Mirror. Like an embittered marriage in which neither partner wants to give up the house, they are locked into a mutually beneficial relationship that both profess to despise.

And as with a marriage, when it gets to court, the demands can turn ugly. When questioned by Campbell's QC, Andrew Caldecott, Morgan explained in detail what he took to be the contract that exists between celebrities and the media. If a celebrity discusses intimate details of her life in the press, argued Morgan, it is an open invitation to the press to examine every intimate detail of that celebrity's life.

When pressed to give an example of Campbell 'invading her own privacy', Morgan cited an article in which she denied that a former boyfriend, Adam Clayton of U2, had spent a weekend in bed with a group of prostitutes. Of course, the logical conclusion to be drawn from that example is that no celebrity in their right mind would ever answer anything but 'no comment' to even the most banal personal inquiry.

In a sense, Morgan is just verbalising what has always been the tacit understanding between celebrities and the media: they talk about their latest film, record, perfume; we ask about their substance abuse and sex addiction. However, because Morgan outlined this trade-off in court, where there is the potential for judicial precedent, it takes on a legal quality that is irresistibly absurd.

Equally, the folly of a publicity-seeking celebrity using the courts to ring-fence his private life was aptly demonstrated by Theakston's failure to prevent the Sunday People from publishing a story about his visit to a brothel. Explaining why he refused Theakston's injunction, Mr Justice Ouseley said he had seen newspaper interviews in which the presenter discussed his private and sexual life. 'The claimant cannot complain,' said the judge, 'if the publicity given to his sexual activities is less favourable in this instance.'

As a result of his unsuccessful application to gag the Sunday People, Theakston did not exactly receive sympathetic press from them. Similarly, Campbell felt the full force of the Mirror's ire as soon as she announced her decision to sue the paper.

Like Theakston and Sara Cox, Campbell is a client of the solicitor Keith Schilling, a veteran entertainment lawyer. In the past, lawyers have usually directed their clients to court only in matters of libel, whereas invasion of privacy was left almost exclusively to the Press Complaints Commission, the industry self-regulator.

Obviously, if the PCC is by-passed in favour of the High Court, its whole privacy code begins to look unnecessary. And it doesn't appear that much more necessary when, as in the case of Cox, the PCC adjudicates a decision, gains a prominent apology, and the complainant still goes to the courts. Cox was photographed naked on her honeymoon on a private island in the Seychelles.

'The PCC needs to be more proactive and better disposed towards the people complaining than they are at present,' Schilling has said. 'The fact the PCC comprises people from the papers themselves does not inspire confidence.'

Guy Black, director of the PCC, counters that in spite of the HRA, the PCC dealt with more complaints last year than ever before. It may, of course, be suggested that an increase in complaints is not necessarily a vote of confidence in the effectiveness of the press at regulating itself.

But Black is not unduly worried. 'Whatever happens in these trials,' he says, 'the strength of the self-regulating system will be enduring.' Perhaps, but the HRA cannot spell good things for the press, and it has arrived without the quid pro quo that, according to Alan Rusbridger, editor of the Guardian, was there to be taken.

Rusbridger had long argued that, given that some kind of privacy law was inevitable, it would have been better for the press to push for reform of the notoriously draconian libel laws. 'I do think if the press in general had thought a bit more clearly about how people would use the HRA, they would have got something in return,' says Rusbridger. 'But,' he adds, 'I think that moment has passed.'

He paints a picture of a slow progression of privacy law through a series of judicial decisions. That means, of course, that there will be plenty of entertaining celebrity cases to come, as the rich and famous make a public display of themselves in the high court in an effort to protect their privacy.

In the process, there will be tears, revelations and accusations, and out of it all there may even arrive some agreement about where public life ends and private life begins. It's impossible to predict where that division will fall. But one guideline might be that celebrities who spend a bit more time being human should also expect to be allowed a bit more time to be anonymous.